1. Field of the Invention
The present invention relates generally to the field of producing oriented films and membranes on a substrate. More particularly, it concerns a method of producing oriented films and membranes by pulsed laser deposition followed by a hydrothermal treatment.
2. Description of Related Art
Thin films composed of molecular sieves have attracted interest because of their potential applications in areas such as separations, catalysis, and sensors. Microporous molecular sieves are attractive materials for membrane-based applications, in part, because of the selective adsorption properties imparted by their uniform pore structure. Microporous molecular sieves offer several advantages over dense inorganic or polymeric thin-film materials which include, for example, high selectivity due to uniform pore size, thermal stability, and facile diffusion. Of particular interest are crystalline films that are oriented in such a way that specific pores define the exposed surface. Preferred crystal orientation offers several advantages in optimizing the efficiencies of gas separations as well as catalytic processes.
A variety of strategies have been developed for the fabrication of continuous films. The deposition and growth of crystals from solution onto a substrate is the most common approach, but this generally results in isolated crystals that must be grown sufficiently large so as to merge and form a continuous film. This aspect can make the preparation of thin films a challenge especially in the nanometer range. Recent efforts in controlling reaction conditions and the use of nanometer-sized seed crystals have improved the quality of some synthesized films and in some cases led to growth of oriented films. For the most part, however, these advancements have been limited to small and medium pore size zeolites such as those with the MFI and LTA topologies.
Many applications proposed for mesoporous molecular sieves would benefit from the ability to fabricate these materials into thin films. Previous attempts to prepare films of the hexagonal one dimensional channel type mesoporous silica, however, have only yielded films in which the pores are oriented parallel to the air/solution or substrate/solution interface.